As catalysts used for producing olefin polymers such as a homopolymer of ethylene or an α-olefin and an ethylene/α-olefin copolymer, catalysts containing a titanium compound supported on a magnesium halide in an active state have been known in the past (the term “polymerization” is sometimes used to include copolymerization hereinafter).
As such olefin polymerization catalysts, catalysts containing titanium tetrachloride or titanium trichloride, which are called Ziegler Natta catalysts, and catalysts comprising a solid titanium catalyst component consisting of magnesium, titanium, halogen and an electron donor and an organometallic compound are widely known.
The latter catalysts exhibit high activity not only in polymerization of ethylene but also in polymerization of α-olefins such as propylene and 1-butene. Further, the resulting α-olefin polymers sometimes have high stereoregularity.
It has been reported in Japanese Patent Laid-Open Publication No. 63310/1982 (patent document 1) and the like that among such catalysts, a catalyst using a solid titanium catalyst component in which an electron donor selected from carboxylic acid esters (typical examples: phthalic acid esters) is supported, an aluminum alkyl compound as a co-catalyst component and a silicon compound having at least one Si—OR (wherein R is a hydrocarbon group) exhibits excellent polymerization activity and stereospecificity.
The polymers obtained by the use of the above catalyst often have narrower molecular weight distribution as compared with polymers obtained by the use of Ziegler Natta catalyst. It is known that polymers having narrow molecular weight distribution tend to have “low melt flowability”, “low melt tension”, “inferior moldability”, “slightly low rigidity”, etc. On the other hand, from the viewpoints of increase of productivity, cost reduction, etc., various high-speed molding techniques, such as high-speed stretching technique having a purpose of increasing productivity of stretched films, have been developed.
If such polymers having relatively narrow molecular weight distribution as above are intended to be stretched at high speed, neck-in or flapping of a film becomes conspicuous because of shortage of melt tension, and increase of productivity sometimes becomes difficult. Therefore, polymers having higher melt tension have been desired in the market.
In order to solve such problems, there have been made a large number of reports, such as reports on a method of preparing polymers of different molecular weights by multi-step polymerization to widen a molecular weight distribution of a polymer (Japanese Patent Laid-Open Publication No. 170843/1993 (patent document 2)), a catalyst containing plural kinds of electron donors (Japanese Patent Laid-Open Publication No. 7703/1991 (patent document 3)) and a catalyst using a succinic acid ester having asymmetric carbon as an electron donor contained in a solid titanium catalyst component (pamphlet of International Publication No. 01/057099 (patent document 4), pamphlet of International Publication No. 00/63261 (patent document 5), pamphlet of International Publication No. 02/30998 (patent document 6)).
On the other hand, in Japanese Patent Laid-Open Publication No. 114811/2001 (patent document 7) and Japanese Patent Laid-Open Publication No. 40918/2003 (patent document 8), a solid catalyst component for polymerization of olefin(s), which is obtained by bringing a titanium compound, a magnesium compound and an electron donating compound into contact with one another, and a catalyst for polymerization of olefin(s), which contains this catalyst component, are disclosed. As this electron donating compound, a 1,2-cyclohexanedicarboxylic acid ester having a trans purity of not less than 80% is used in the invention described in the patent document 7, and a cyclohexenedicarboxylic acid diester is used in the invention described in the patent document 8. As an example of this cyclohexenedicarboxylic acid diester, only a 1-cyclohexenedicarboxylic acid diester wherein an alkoxycarbonyl group is bonded to the first position and the second position of a cyclohexene ring of 1-cyclohexene is disclosed (paragraphs “0021” to “0024”, and working examples). In the patent documents 7 and 8, however, there is no description of molecular weight distribution of an olefin polymer.
The present applicant has disclosed in a pamphlet of International Publication No. 2006/077945 that a solid titanium catalyst component containing a specific cyclic ester compound as an electron donor component gives an olefin polymer having an extremely wide molecular weight distribution (patent document 9).
Patent document 1: Japanese Patent Laid-Open Publication No. 63310/1982
Patent document 2: Japanese Patent Laid-Open Publication No. 170843/1993
Patent document 3: Japanese Patent Laid-Open Publication No. 7703/1991
Patent document 4: pamphlet of International Publication No. 01/057099
Patent document 5: pamphlet of International Publication No. 00/63261
Patent document 6: pamphlet of International Publication No. 02/30998
Patent document 7: Japanese Patent Laid-Open Publication No. 114811/2001
Patent document 8: Japanese Patent Laid-Open Publication No. 40918/2003
Patent document 9: pamphlet of International Publication No. 2006/077945